New high pressure die casting aluminum alloy for high temperature and corrosive applications

ABSTRACT

Copper-free aluminum alloys suitable for high pressure die casting and capable of age-hardening under elevated temperatures. The alloy includes about 7-15 wt % silicon, about 0 to 0.6 wt % magnesium, about 0 to 1.0 wt % iron, about 0 to 1.0 wt % manganese, about 0 to 1.0 wt % zinc, about 0 to 0.1 wt % strontium, about 0 to 0.5 wt % titanium, about 0 to 0.5 wt % zirconium, about 0 to 0.5 wt % vanadium, about 0 to 0.5 wt % copper, and about 0 to 1.0 wt % nickel, with a balance of aluminum. Methods for making high pressure die castings and castings manufactured from the alloy.

FIELD OF THE INVENTION

The invention relates generally to a low copper (Cu) or Cu-free aluminumalloy formulated for high pressure die casting (HPDC), and the castingstherefrom, which are capable of age-hardening at elevated temperatureswith reduced porosity, thus possessing superior mechanical propertiesfor applications particularly in the automotive industry.

BACKGROUND OF THE INVENTION

HPDC is a cost-effective and wide-spread method for industrialproduction of metal components requiring precise dimensionalconsistency, low dimensional tolerances and where a smooth surfacefinish is important. Manufacturers in the car industry are nowincreasingly required to produce near-net-shape aluminum components witha combination of high tensile properties and ductility, and HPDC affordsthe most economic production method for large-scale quantities of smallto medium sized components.

In order to avoid discontinuities in the cast component, the moltenalloy is injected into the die cavity rapidly enough that the entirecavity fills before any portion of the cavity begins to solidify. Hence,the injection is under high pressure and the molten metal is subject toturbulence as it is forced into a die and then rapidly solidifies.Unfortunately, since the air being replaced by the molten alloy haslittle time to escape, some of it is trapped and porosity results.Castings also contain pores resulting from gas vapor decompositionproducts of the organic die wall lubricants and porosity may also resultfrom shrinkage during solidification. A major drawback of the porosity,particularly induced from entrapped air or gas vapor, resulting from theHPDC process is that castings made from aluminum alloys which ordinarilyhave the capacity to respond to age-hardening cannot be effectivelyartificially aged, that is, they cannot attain high supersaturation ofhardening elements such as Mg or Cu in the solution prior to artificialaging because no traditional solution treatment can be applied to highpressure die casting parts. The internal pores containing gases or gasforming compounds in the high pressure die castings expand duringconventional solution treatment at elevated temperatures, resulting inthe formation of surface blisters on the castings. The presence of theseblisters affects not only the appearance of castings but alsodimensional stability and in some cases it can negatively impactparticular mechanical properties of HPDC components. Specifically,aluminum alloy HPDC cast parts are not amenable to solution treatment(T4) at a high temperature, for example 500° C., which significantlyreduces the potential of precipitation hardening through a full temperT6 and/or T7 (equivalently phrased as a combination of temper T4 and T5)heat treatment. As such, it is nearly impossible to find aconventionally processed HPDC component without large gas bubbles.

In Al—Si casting alloys (e.g., alloys 319, 356, 390, 360, 380),strengthening is achieved through heat treatment after casting, withaddition of various alloying hardening solutes including, but notlimited to, Cu and Mg. The heat treatment of cast aluminum involves amechanism described as age hardening or precipitation strengthening.Heat treatment (conventional T6 and/or T7 heat treatment) generallyincludes at least one or a combination of three steps: (1) solutiontreatment (also defined as T4) at a relatively high temperature belowthe melting point of the alloy, often for times exceeding 8 hours ormore to dissolve its alloying (solute) elements and to homogenize ormodify the microstructure; (2) rapid cooling, or quenching into a coldor warm liquid medium after solution treatment, such as water, to retainthe solute elements in a supersaturated solid solution; and (3 )artificial aging (T5) by holding the alloy for a period of time at anintermediate temperature suitable for achieving hardening orstrengthening through precipitation. Solution treatment (T4) servesthree main purposes: (1) dissolution of elements that will later causeage hardening, (2) spherodization of undissolved constituents, and (3)homogenization of solute concentrations in the material. Quenching afterT4 solution treatment retains the solute elements in a supersaturatedsolid solution (SSS) and also creates a supersaturation of vacanciesthat enhances the diffusion and the dispersion of the precipitates. Tomaximize the strength of the alloy, the precipitation of allstrengthening phases should be prevented during quenching. Aging (T5,either natural or artificial aging) creates a controlled dispersion ofstrengthening precipitates.

With T5 aging, there generally are three types of aging conditions,which are commonly referred as underaging, peak aging and over aging. Atpre-aging, or an initial stage of aging, Guinier-Preston (GP) zones andfine shearable precipitates form, and the casting is considered to beunderaged. In this condition, mechanical properties of the casting, forexample material hardness and yield strength, are usually low. Increasedtime at a given temperature or aging at a higher temperature furtherevolves the precipitate structure increasing mechanical properties suchas hardness and yield strength to maximum levels for achieving the peakaging/hardness condition. Further aging decreases the hardness/yieldstrength and the casting becomes overaged due to precipitate coarseningand its transformation of crystallographic incoherency.

Considering that the conventional HPDC aluminum components inevitablycontain internal porosity, artificial aging (T5) becomes a veryimportant step in achieving the desired mechanical properties withoutcausing blistering. The strengthening that results from aging occursbecause the retained hardening solutes present in the supersaturatedsolid solution form precipitates that are finely dispersed throughoutthe grains and that increase the ability of the casting to resistdeformation by slip and plastic flow. Maximum hardening or strengtheningmay occur when the aging treatment leads to the formation of a criticaldispersion of at least one type of these fine precipitates.

In addition, in conventional HPDC processes the cast parts are oftenslowly cooled to a low temperature, for example, below 200° C., prior todie ejection and quench. This significantly diminishes the subsequentaging potential since the hardening solute solubility decreasessignificantly with decreasing quench temperature. As a result, theremaining hardening solute, such as Cu and Mg, available in the aluminummatrix for subsequent aging hardening is very limited. Although an alloymay contain 3˜4% Cu in nominal composition, most of the Cu combines withother elements to form intermetallic phases. Without solution treatment,the Cu-containing intermetallic phases will not contribute to agehardening of the material. Therefore, addition of Cu in the current HPDCalloys used in production is not effective in terms of both propertyimprovement and quality assurance.

Typical Al—Si based HPDC alloys contain about 3˜4% Cu. It is generallyaccepted that copper (Cu) has the single greatest impact of all alloyingsolutes/elements on the strength and hardness of aluminum alloycastings, both heat-treated and not heat-treated and at both ambient andelevated service temperatures. Cu is known to improve the machinabilityof alloys by increasing matrix hardness, making it easier to generatesmall cutting chips and fine machined finishes. On the downside, Cuincreases the alloy freezing range and decreases feeding capability,leading to a high potential for shrinkage porosity. More significantly,it generally reduces the corrosion resistance of aluminum castings; andin certain alloys and tempers, it increases stress corrosionsusceptibility. For example, it has been reported that aluminum alloyswith a high Cu content (i.e., above about 3-4%) have experienced anunacceptable rate of corrosion, especially in salt-containingenvironments. Typical high pressure die (HPDC) aluminum alloys, such asA 380 or 383, which are used for transmission and engine parts, contain2-4% Cu. It can be anticipated that the corrosion issue of these alloyswill become more significant, particularly when longer warranty time andhigher vehicle mileages are required.

Aluminum alloys have been developed to address some of the knownproblems. For example, Aluminum alloy A380 is a generally age-hardenablealloy with the composition (in wt. %) 9 Si, 3.1 Cu, 0.86 Fe, 0.53 Zn,0.16 Mn, 0.11 Ni and 0.11 Mg (Lumley, R.N. et al. “Thermalcharacteristics of heat-treated aluminum high-pressure die-castings” 1Scripta Materialia 58 (2008) 1006-1009, the entire disclosure of whichis incorporated herein by this reference). It is known that theCu-phases, such as the Al₂Cu precipitate phase, are important toachieving the benefits of artificial aging, as well as for improvingthermal conductivity of the casted part. However the castings sufferfrom lower corrosion resistance, a high potential for cast defects and ahigh material cost due to the Cu.

It is known that reducing the Cu content improves the corrosionresistance of an aluminum alloyed material. However Cu is thought to bea necessary hardening component in HPDC aluminum castings. In previouslypublished work, some of the present inventors recommended lower Cucontent ranges of 0.5% to 1.5% by weight depending upon the as-cast andheat treatment conditions (see U.S. application Ser. No.12/827,564,publication No. 20120000578, the entire disclosure of which isincorporated herein by this reference). Nonetheless the presence of Cuin the casting solution after solidification was considered integral tothe preservation of acceptable mechanical properties, in particularhardness/yield strength of the cast.

Essentially Cu-free alloys, such as A356, are known in the art, howeverthey are typically used in sand casting and/or semi-permanent moldcasting processes other than HPDC and as formulated, suffer fromdeficiencies in mechanical properties such as tensile strength.

Lin (U.S. patent application Ser. No. 11/031,095) discloses an aluminumalloy having reduced a reduced Cu percentage; however Lin nonethelessteaches the importance of presence of some Cu to the hardening process.Moreover, the Lin alloy formulations and castings contain low weightpercentages of Si in order to avoid brittle Al—Si eutectic networks inthe casted condition. The goal of Lin was to produce aluminum alloyssuitable for thixoforming, a molding process which combines features ofcasting and forging involving low- pressure molding to produceparticular microcrystalline structures and to avoid solution heattreatment. The alloys of Lin would be unsuitable for HPDC methods.

Clearly a need exists in the art for an aluminum alloy suitable for HPDCand amenable to age hardening, without compromising corrosion resistanceor mechanical properties of the cast components.

SUMMARY OF THE INVENTION

Accordingly, the present disclosure provides substantially Cu-free orlow-Cu aluminum alloys suitable for high pressure die casting andage-hardening at elevated temperatures with reduced porosity compared toknown HPDC aluminum alloys. The castings exhibit enhanced mechanicalproperties for both room and elevated temperature structuralapplications.

An aluminum alloy according to invention is suitable for high pressuredie casting processes and is capable of age hardening, providingsuperior mechanical properties after age hardening at elevatedtemperatures. Embodiments of the aluminum alloy comprise by weight about7 to about 15% silicon (Si); about 0 to about 0.6% magnesium (Mg); about0 to about 1% iron (Fe); about 0 to about 1% manganese (Mn); about 0 toabout 1.0% zinc (Zn); about 0 to about 0.1 weight percent strontium(Sr); about 0 to about 0.5 weight percent titanium (Ti); and about 0 toabout 0.5% zirconium (Zr) and at least about 78% aluminum. An alloy mayfurther comprise about 0 to about 0.5% vanadium (V). An alloy accordingto the disclosure may also include about 0 to about 0.5% copper (Cu);and about 0 to about 1% nickel (Ni). The above composition ranges may beadjusted based on performance requirements.

Other embodiments are directed to HPDC articles cast from an aluminumalloy according to the invention. An aluminum alloy is formulated suchthat the alloy exhibits corrosion of less than about 0.1 millimeter peryear. An aluminum alloy is formulated such that the alloy being as-cast,age-hardened by temper T5 treatment, and soaked at 200° C. for 200 hoursand tested at 200° C. exhibits a yield strength above about 150 MPa,ultimate tensile strength above about 190 MPa, and strain above about1.8 percent. The alloy is capable of receiving solution treatment over aperiod generally less than what other aluminum alloys require. Theseembodiments would not experience blistering, and would be able toundergo effective temper or T6/T7 age-hardening treatments. Embodimentsdirected to cast articles possess superior mechanical properties whensubjected to one or more steps of age-hardening temper treatments.

Further embodiments are directed to methods for manufacturing articlesby HPDC of an aluminum alloy according to the invention. The methodscomprise providing a molten aluminum alloy according to embodiments ofthe invention, injecting the molten aluminum alloy into a die under highpressure, solidifying the alloy in the die to form the casting, coolingthe casting in the die to a quenching temperature, quenching the castingin a quenching solution, and subjecting the casting to one or moreage-hardening treatments. The alloy is formulated such that the castingcorrodes at a rate of less than about 0.1 millimeter per year andmaintains a yield strength above about 150 MPa, ultimate tensilestrength above about 190 MPa, and strain above about 1.8 percent afterit is soaked at 200° C. for 200 hours and tested at 200° C.

These and additional aspects and embodiments will be more clearlyunderstood in view of the detailed description and figures set forthbelow.

BRIEF DESCRIPTION OF THE FIGURES

The following detailed description of specific embodiments can be bestunderstood when read in conjunction with the following drawings:

FIG. 1. sets forth a calculated phase diagram of a cast aluminum alloyknown in the art (A380 HPDC alloy) showing phase transformations as afunction of Cu content.

FIG. 2. sets forth a chart displaying the porosity increases of thepresent work in relation to the Cu level according to a specificembodiments of the invention.

FIG. 3. sets forth empirical data comparing the chemical composition ofT5 HPDC alloys A380, A360 and an embodiment according to the inventioncomparing tensile properties and corrosion resistance and corrosionconductivity in samples taken from.

FIG. 4. sets forth tabled empirical data comparing tensile properties inas-cast, T5-aged, and soaked HPDC samples cast from known alloy A360,A380, and one specific alloy embodiment according to the invention.

FIG. 5. sets forth tabled empirical data comparing tensile properties inas-cast, T5-aged, and soaked HPDC samples cast from known alloy A360,A380, and another specific alloy embodiment according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the disclosure relate generally to substantially Cu-freeor low-Cu aluminum alloys formulated to provide HPDC casted componentscapable of age-hardening at elevated temperatures and exhibitingsuperior mechanical properties and reduced porosity. Unlikealuminum-based Cu containing alloy castings known in the art, thepresent castings are capable of a full range of temper age-hardeningtreatments.

As used herein, “castings” refer generally to aluminum alloy highpressure die castings formed through solidification of aluminum alloycompositions. Thereby, the castings may be referred to herein during anystage of a high pressure die casting process and/or a heat treatmentprocess subsequent to solidification, whether cooling, quenching, aging,or otherwise. Further, castings may include any part, component, productformed via an embodiment of the present invention.

Further, as used herein, “mechanical property,” and related phrasesthereof, refer generally to at least one and/or any combination of,strength, hardness, toughness, elasticity, plasticity, brittleness, andductility and malleability that measures how a metal, such as aluminumand alloys thereof, behaves under a load. Mechanical propertiesgenerally are described in terms of the types of force or stress thatthe metal must withstand and how these are resisted.

As used herein, “strength” refers to at least one and/or any combinationof yield strength, ultimate strength, tensile strength, fatiguestrength, and impact strength. Strength refers generally to a propertythat enables a metal to resist deformation under a load. Yield strengthrefers generally to the stress at which a material begins to deformplastically. In engineering, the yield strength may be defined as thestress at which a predetermined amount (for instance about 0.2%) ofpermanent deformation occurs. Ultimate strength refers generally to amaximum strain a metal can withstand. Tensile strength refers generallyto a measurement of a resistance to being pulled apart when placed in atension load. Fatigue strength refers generally to an ability of a metalto resist various kinds of rapidly changing stresses and may beexpressed by the magnitude of alternating stress for a specified numberof cycles. Impact strength refers generally to the ability of a metal toresist suddenly applied loads. Generally, the higher the yield strength,the higher the other strengths are as well.

As used herein, “hardness” refers generally to a property of a metal toresist permanent indentation. Hardness generally is directlyproportional to strength. Thus, a metal having a high strength alsotypically has high hardness.

Aluminum alloy compositions solidified to form castings are known tocomprise a number of elements, such as, but not limited to, aluminum(Al), silicon (Si), magnesium (Mg), copper (Cu), iron (Fe), manganese(Mn), zinc (Zn), nickel (Ni), titanium (Ti), strontium (Sr), etc. Theelements and their respective concentrations that define an aluminumalloy composition may affect significantly the mechanical properties ofthe casting formed therefrom. More particularly, some elements may bereferred to as hardening solutes. These hardening solutes may engageand/or bond among themselves and/or with other elements duringsolidification, cooling, quenching, and aging of casting and heattreatment processes. Aging generally is used to strengthen castings.While, various processes for aging are available, generally only someare applicable and/or sufficiently effective for aluminum alloy highpressure die casting processes, for reasons described above. Aluminumalloy castings known to the HPDC parts have generally been limited totemper T5 treatment aging (natural or artificial). Aging strengthenscastings by facilitating the precipitation of the hardening solutes ofthe aluminum alloy composition.

Artificial aging (T5) heats the castings to an elevated, typicallyintermediate, temperature for a length of time sufficient to strengthenthe casting through precipitation of the hardening solutes. Sinceprecipitation is a kinetic process, the respective concentrations(supersaturation) of the hardening solutes available for precipitationare significant to the casting's strengthening response to aging.Therefore, the concentrations of hardening solutes, and the availabilitythereof for precipitation, significantly impact the extent to which thecasting is strengthened during aging. If the hardening solutes areprevented, or substantially prevented, from bonding among themselvesand/or with other elements prior to the aging, then the hardeningsolutes may precipitate during aging to strengthen the casting.

To prevent, or at least substantially prevent, the hardening solutesfrom bonding among themselves and/or with other elements of the aluminumalloy composition prior to aging and, thereby, maintain the availabilityof the hardening solutes, the casting is cooled to a quenchingtemperature in the die and quenched immediately thereafter. Tofacilitate the cooling of the casting to the quenching temperature, anembodiment may comprise selectively heating and/or cooling one or moredesignated areas of the casting prior to its removal from the die forquenching.

Further, to increase precipitation during aging, and, thereby, enhancemechanical properties of castings, one or more specific hardeningsolutes typically are incorporated into the aluminum alloy composition.Traditionally it has been accepted in the art that magnesium (Mg),copper (Cu), and silicon (Si) are particularly effective and evennecessary as hardening solutes in aluminum alloys. Mg may combine withSi to form Mg/Si precipitates, such as β″, β′, and equilibrium Mg₂Siphases. The precipitate types, sizes, and concentrations typicallydepend on the present aging conditions and the compositions of thealuminum alloys. For example, under-aging tends to form shearable β″precipitates, while peak-aging and over-aging generally form unshearableβ′ and equilibrium Mg₂Si phases. When aging aluminum alloys, Si alonecan form Si precipitates. Si precipitates, however, generally are not aseffective as Mg/Si precipitates in strengthening aluminum alloys.Further, Cu can combine with aluminum (Al) to form multiple metastableprecipitate phases, such as θ′ and θ, in Al—Si—Mg—Cu alloys, which areknown to be very effective in strengthening.

It is also widely accepted that increased concentrations of the moreeffective hardening solutes may be incorporated into the aluminum alloycomposition to increase their availability for precipitation at aging.According to specifications for conventional aluminum alloy compositionsfor HPDC, generally the maximum Mg concentration incorporated is lessthan 0.1% by weight of the respective compositions. In industrypractice, however, the Mg concentrations in such aluminum alloycompositions tend to be much lower than 0.1%. As a result, thecompositions generally have an inability to form Mg/Si precipitates and,as such, minimal strengthening of the casting through Mg/Siprecipitation results, even during T5 aging processes. In fact, it isgenerally accepted that the only feasible strengthening of the castingin this case results through formation of Al/Cu precipitates. Cu,therefore, has been considered a necessary hardening solute inaluminum-silicon alloys in HPDC operations.

However, when subjecting an HPDC casting to desirable age-hardeningtemper treatments, the hardening efficacy and contribution of Cu may besurprisingly limited. Although typical HPDC aluminum alloys, such asA380, 380 or 383, contain 3˜4% Cu in nominal composition, the actual Cusolute remaining in as-cast aluminum matrix for the subsequent aging isactually much reduced. As shown in FIG. 1, the Cu content in thealuminum matrix is only about 0.006% even when the casting is quenchedat about 200° C. A majority of the Cu is tied up during solidificationwith Fe and other elements forming intermetallic phases which have noaging responses if the components/parts do not undergo high temperaturesolution treatment. In this case, the role the Cu-containingintermetallic phases play in the strain-hardening is similar to othersecond phase particles like Si. The contribution of Cu to the aginghardening in the conventional high pressure die casting parts isactually negligible. Therefore, contrary to convention regarding theimportance of Cu as a hardening solute, the present inventors discoveredthat Cu may be removed from the alloy if the composition is otherwiseformulated within particular parameters to achieve substantially Cu-freealuminum alloys which provide HPDC castings with greater corrosionresistance, and some superior mechanical properties. Otherwise, smallamounts of Cu may be utilized in the alloy to maintain some of thebenefits it contributes. It should also be noted that Mg has highdiffusivity in Al—Si alloy. Since the alloy only needs to diffuse Mg andSi particles in solution treatment, the solution treatment time can beshortened. The low-Cu and Cu-free embodiments discussed herein providethis advantage of shortened treatment time. This additionally allows foreffective temper treatment or T6/T7 age-hardening treatments.

FIG. 2 depicts a chart comparing the volume fraction of porosity to theCu level in an alloy according to one embodiment of the presentinvention. Also shown for the comparison are some data points from thework of prior art as is shown, the porosity increases significantly whenCu is between 0.5 and 0.8 weight percent. Within this range, the volumefraction of porosity increases from about 0.4 percent to about 0.6percent. Above this range, the porosity levels around 0.7 percent. Belowthis range, the porosity also increases significantly, but is stillwithin an expected range. The reduced porosity levels present when theCu level is within the range anticipated by the present invention, fromabout 0 to about 0.5 weight percent, ensures the improved performance ofthe alloy.

Accordingly, one embodiment of the invention provides an aluminum alloysuitable for HPDC processes and capable of temper age-hardening atelevated temperatures. The alloy comprises at least about 78 weightpercent aluminum (Al); about 7 to about 15 weight percent silicon (Si);about 0 to about 0.6 weight percent magnesium (Mg); about 0 to about 1weight percent iron (Fe); about 0 to about 1 weight percent manganese(Mn); about 0 to about 1.0 weight percent zinc (Zn); about 0 to about0.1 weight percent strontium (Sr); about 0 to about 0.5 weight percenttitanium (Ti); and about 0 to about 0.5 weight percent zirconium (Zr).Mg and Si are effective hardening solutes. Mg combines with Si to formMg/Si precipitates such as β″, β′ and equilibrium Mg₂Si phases. Theactual precipitate type, amount, and sizes depend on aging conditionsand particularly the Mg and Si content remained in the matrix aftercasting. Compared with Cu, the solubility of Si and Mg in aluminummatrix is higher. Also, the diffusivity of Mg and Si in the aluminummatrix is higher than Cu. Increasing Si near the eutectic composition(˜12%) can also help reduce freezing range and thus increase castabilityand quality of the casting. Mg and Si are both lighter and morecost-effective than Cu.

Ideally, a Cu-free aluminum alloy should produce a similar quantity ofsecond phase particles in the microstructure after solidification. Thealloy also should contain iron (Fe) to avoid die soldering. Fe, however,can easily form an undesirable needle-shape intermetallic phase ifmanganese (Mn) is not added in appropriately proportional amounts.

According to other embodiments, the aluminum alloy further comprises:about 0 to about 0.5 weight percent vanadium (V). According to a veryspecific embodiment, an aluminum alloy suitable for HPDC and capable ofage-hardening consists essentially of: about 13 weight percent silicon(Si); about 0.4 weight percent magnesium (Mg); about 0.4 weight percentiron (Fe); about 0.8 weight percent manganese (Mn); about 0.5 weightpercent zinc (Zn); about 0.04 weight percent strontium (Sr); about 0.3weight percent titanium (Ti); about 0.15 weight percent zirconium (Zr);and a balance of aluminum (Al). According to another very specificembodiment, an aluminum alloy suitable for HPDC and capable ofage-hardening consists essentially of: about 8.5 weight percent silicon(Si); about 0.4 weight percent magnesium (Mg); about 0.4 weight percentiron (Fe); about 0.5 weight percent manganese (Mn); about 0.5 weightpercent zinc (Zn); about 0.04 weight percent strontium (Sr); about 0.3weight percent titanium (Ti); about 0.3 weight percent zirconium (Zr);about 0.3 weight percent vanadium (V); and a balance of aluminum (Al).According to another very specific embodiment, an aluminum alloysuitable for HPDC and capable of age-hardening consists essentially of:about 0 to about 0.5 weight percent copper (Cu); and about 0 to about 1weight percent nickel (Ni).

According to a very specific embodiment, an aluminum alloy suitable forHPDC and capable of age-hardening consists essentially of: at leastabout 78 to about 90 weight percent aluminum (Al); about 7 to about 15weight percent silicon (Si); about 0 to about 0.6 weight percentmagnesium(Mg); about 0 to about 1 weight percent iron (Fe); about 0 toabout 1 weight percent manganese (Mn); about 0 to about 1.0 weightpercent zinc (Zn); about 0 to about 0.1 weight percent strontium (Sr);about 0 to about 0.5 weight percent titanium (Ti); about 0 to about 0.5weight percent zirconium (Zr); about 0 to about 0.5 weight percentvanadium (V); about 0 to about 0.5 weight percent copper (Cu); and about0 to about 1 weight percent nickel (Ni).

The table of FIG. 3 sets forth a comparison of the calculated quantityranges of second phase chemicals between an illustrative embodimentsaccording to the invention and several conventional HPDC alloys,including A380, 383, and 360, as well as two proprietary alloys, P011783and P020385. As can be seen from the table, the array of particles isunique to this invention, and maintains relatively low amounts of mostparticles, including Cu. Other particles, including Mn and Ni, areutilized in larger quantities than in the other depicted alloys.Likewise, while Sn is used in most of the other alloys, it is not foundin the present invention. Additionally, Ti, Sr, and Zr are not used inthe A380, 383, or 360 alloys, but are represented by the presentinvention. Finally, the particle vanadium (V), is not found in any ofthe alloys except the new composition. The embodiments of the presentinvention are capable of use for high temperature and corrosiveapplications, as well as having improved mechanical properties. The newalloy offers the best combination of good castability, high mechanicalproperties particularly at elevated temperatures, and corrosionresistance. Also, the new alloy reduces the alloy density, material, andmanufacturing cost whole improving integrity of HPDC aluminum castingsand performance. The new alloy is also expected to reduce aluminumcasting product development cycles and time to market.

Referring to the certain specific embodiments, the use of some elementsin the present application is uncommon for aluminum alloys. Strontiumhas been used in aluminum alloys to improve ductility and die solderingresistance. Strontium is known to modify the aluminum-silicon eutectic,which can be achieved at very low levels. However, it is desirable toavoid using higher addition levels, as they are associated with castingporosity. Likewise, titanium is an element that may be added to analuminum alloy as a grain refiner, as well as improving thestrength-to-weight ratio and corrosion resistance. Titanium can also beincluded at concentrations greater than those required for grainrefinement to reduce cracking tendencies and to improve high temperatureperformance. Zirconium is used in alloys largely for its corrosionresistance and high temperature performance. Forming a fineintermetallic precipitate that inhibits recovery and recrystalization isanother effect of zirconium addition to the alloy. Finally, vanadium isgenerally known for resisting corrosion, and can be used as a stabilizerin an aluminum alloy. It has also been found to significantly improveother properties, such as strength in jet engines and airframes.

A key benefit afforded by the inventive alloys is that the corrosionproblems known in the art as associated with Cu content may beeliminated or greatly reduced without compromising the strength of theHPDC cast article. The use of no-, or low-Cu in the alloy largelyresolved this issue. FIG. 4 and FIG. 5 further illustrate this point.FIG. 4 is a tabled collation of data generated in an experiment testingand comparing HPDC cast samples, T5 samples, and T5 and soaked samples,from known HPDC A380 and A360 alloys and specific alloy embodiment #1according to the invention. For the T5 data, the casts were subject toT5 aging. Compositions, tensile properties of the castings, andcorrosion conductivity data are all displayed for comparison purposes.FIG. 5 is a tabled collation of data generated in an experiment testingand comparing HPDC cast samples, T5 samples, and T5 and soaked samples,from known HPDC A380 and A360 alloys and specific alloy embodiment #2according to the invention. Inspection of the data reveals that bothembodiment #1 and #2, which do not contain Cu, possess much bettercorrosion resistance compared with the existing HPDC alloys exemplifiedby A380 and A360. Experiencing corrosion of less than about 0.1millimeters per year, or between about 0.09 and 0.07 millimeters peryear, is expected for certain embodiments of this invention. Further,embodiments #1 and #2 have better as-cast tensile properties, and betteraging response and thus higher tensile strengths after T5 heat treatmentin comparison with exemplary HPDC alloys A380 and A360. Additionally,the T5 samples after being further soaked at 200° C. for 200 hours andtested at 200° C., the properties of the present formulations areimproved over the A380 and A360 alloys, as is depicted. For each of allof the samples have yield strength above about 150 MPa, ultimate tensilestrength above about 190 MPa, and strain above about 1.8 percent.Notably the alloy according to the invention is also slightly lighterproviding an additional cost efficiency benefit.

According to another embodiment, an HPDC article cast from asubstantially Cu-free aluminum alloy formulated according to thedisclosure is provided. Unlike conventionalCu-containing alloys, theCu-free or low-Cu alloy may undergo a very short (i.e. 10 minutes) T4solution treatment without causing blister problem, to produce effectivetemper or T6/T7 age-hardening treatments. In comparison with Cu, Mg hashigh diffusivity in Al—Si alloy and thus requires much shorter solutiontreatment time. Due to the absence of Cu in the present invention, orsignificantly lower levels of Cu, only the Mg and Si participles need todissolve during solution treatment. Therefore the present invention,having relatively higher concentrations of Mg and Si and relativelylower concentrations of Cu, is capable of a shortened solutiontreatment. In specific embodiments, the cast article may besolution-treated at treatment temperatures of around 500° C. Accordingto the present invention, Mg₂Si particle dissolution during solutiontreatment can be completed with 25 minutes at 450° C. even for thelargest particle size of 10 um. Generally, for HPDC parts, the typicalMg₂Si particle size is less than 5 um, even in thick section, such asthe bulk head area of an engine block. In one embodiment of the presentinvention, solution treatment of the die cast parts with the disclosedalloys can be solution-treated in as short as 5 minutes. The castarticle may exhibit a microstructure comprising at least one or more ofthe insoluble solidified and/or precipitated particles with at least onealloying element selected from the group consisting of Al, Si, Mg, Fe,Mn, Zn, Sr, Ti, Zr, V, Cu, Ni.

According to other embodiments, an HPDC manufacturing process isprovided wherein a molten substantially Cu-free or low-Cu aluminum alloyis provided and cast into a die under high pressure. The alloysolidifies in the die to form the casting, and the casting in the die ispermitted to cool to a desired quenching temperature, which is generallyempirically determined. The casting may be removed from the die andquenched in a quenching solution. The casting may be subject to one ormore steps of age-hardening temper treatments. The casting may also besubjected to solution heat treatment for a time from about 5 minutes toabout 25 minutes. This treatment may be performed after quenching thecasting and before subjecting the casting to at least one age-hardeningtreatment. Alternatively, this short solution treatment may be performedimmediately after the casting is made and ejected from the die while thecasting is still heated to save energy and reduce cost when reheating.

According to very specific embodiments, the method of manufacturing ahigh pressure die casting of an aluminum alloy comprises: providing amolten aluminum alloy consisting essentially of at least about 78 toabout 90 weight percent aluminum (Al), about 7 to about 15 weightpercent silicon (Si), about 0 to about 0.6 weight percent magnesium(Mg), about 0 to about 1 weight percent iron (Fe); about 0 to about 1weight percent manganese (Mn), about 0 to about 1.0 weight percent zinc(Zn), about 0 to about 0.1 weight percent strontium (Sr), about 0 toabout 0.5 weight percent titanium (Ti), about 0 to about 0.5 weightpercent zirconium (Zr), about 0 to about 0.5 weight percent vanadium(V), about 0 to about 0.5 weight percent copper (Cu), and about 0 toabout 1 weight percent nickel (Ni); casting the molten aluminum alloyinto a die under high pressure; solidifying the alloy in the die to formthe casting; cooling the casting still in the die to a quenchingtemperature; quenching the casting in a quenching solution; andsubjecting the casting to a T5 age-hardening treatment.

It is noted that terms like “generally,” “commonly,” and “typically,”when utilized herein, are not utilized to limit the scope of the claimedembodiments or to imply that certain features are critical, essential,or even important to the structure or function of the claimedembodiments. Rather, these terms are merely intended to identifyparticular aspects of an embodiment or to emphasize alternative oradditional features that may or may not be utilized in a particularembodiment.

For the purposes of describing and defining embodiments herein it isnoted that the terms “substantially,” “significantly,” and“approximately” are utilized herein to represent the inherent degree ofuncertainty that may be attributed to any quantitative comparison,value, measurement, or other representation. The terms “substantially,”“significantly,” and “approximately” are also utilized herein torepresent the degree by which a quantitative representation may varyfrom a stated reference without resulting in a change in the basicfunction of the subject matter at issue.

Having described embodiments of the present invention in detail, and byreference to specific embodiments thereof, it will be apparent thatmodifications and variations are possible without departing from thescope of the embodiments defined in the appended claims. Morespecifically, although some aspects of embodiments of the presentinvention are identified herein as preferred or particularlyadvantageous, it is contemplated that the embodiments of the presentinvention are not necessarily limited to these preferred aspects.

What is claimed:
 1. An aluminum alloy suitable for high pressure diecasting and capable of temperature-elevated age-hardening, the alloycomprising: at least about 78 weight percent aluminum (Al); about 7 toabout 15 weight percent silicon (Si); about 0 to about 0.6 weightpercent magnesium (Mg); about 0 to about 1 weight percent iron (Fe);about 0 to about 1 weight percent manganese (Mn); about 0 to about 1.0weight percent zinc (Zn); about 0 to about 0.1 weight percent strontium(Sr); about 0 to about 0.5 weight percent titanium (Ti); and about 0 toabout 0.5 weight percent zirconium (Zr).
 2. The alloy according to claim1, further comprising: about 0 to about 0.5 weight percent vanadium (V).3. The aluminum alloy according to claim 1, the alloy comprising; about13 weight percent silicon (Si); about 0.4 weight percent magnesium (Mg);about 0.4 weight percent iron (Fe); about 0.8 weight percent manganese(Mn); about 0.5 weight percent zinc (Zn); about 0.04 weight percentstrontium (Sr); about 0.3 weight percent titanium (Ti); about 0.15weight percent zirconium (Zr); and a balance of aluminum (Al).
 4. Thealuminum alloy according to claim 2, the alloy comprising; about 8.5weight percent silicon (Si); about 0.4 weight percent magnesium (Mg);about 0.4 weight percent iron (Fe); about 0.5 weight percent manganese(Mn); about 0.5 weight percent zinc (Zn); about 0.04 weight percentstrontium (Sr); about 0.3 weight percent titanium (Ti); about 0.3 weightpercent zirconium (Zr); about 0.3 weight percent vanadium (V); and abalance of aluminum (Al).
 5. The alloy according to claim 1, furthercomprising: about 0 to about 0.5 weight percent copper (Cu); and about 0to about 1 weight percent nickel (Ni).
 6. A high pressure die castarticle, cast from an aluminum alloy according to claim
 1. 7. The castarticle according to claim 6 having undergone age-hardening at elevatedtemperature.
 8. The cast article according to claim 6, wherein the castarticle undergoes a solution heat treatment for a time from about 5minutes to about 25 minutes.
 9. The cast article according to claim 7,exhibiting corrosion of less than about 0.1 mm/year.
 10. The castarticle according to claim 7, wherein age-hardening conditions comprisean effective temper, T6, or T7 treatments.
 11. The cast articleaccording to claim 7, wherein the cast article being as-cast,age-hardened by a temper T5 treatment, or age-hardened by a temper T5treatment and then soaked at 200° C. for 200 hours and tested at 200° C.exhibits a yield strength above about 150 MPa, ultimate tensile strengthabove about 190 MPa, and strain above about 1.8 percent.
 12. The castarticle according to claim 10, wherein the cast article issolution-treated at a temperature around 500° C.
 13. An aluminum alloysuitable for high pressure die casting and capable of age-hardening, thealloy consisting essentially of: at least about 78 to about 90 weightpercent aluminum (Al); about 7 to about 15 weight percent silicon (Si);about 0 to about 0.6 weight percent magnesium(Mg); about 0 to about 1weight percent iron (Fe); about 0 to about 1 weight percent manganese(Mn); about 0 to about 1.0 weight percent zinc (Zn); about 0 to about0.1 weight percent strontium (Sr); about 0 to about 0.5 weight percenttitanium (Ti); about 0 to about 0.5 weight percent zirconium (Zr); about0 to about 0.5 weight percent vanadium (V); about 0 to about 0.5 weightpercent copper (Cu); and about 0 to about 1 weight percent nickel (Ni).14. A high pressure die cast article, cast from an aluminum alloyaccording to claim
 13. 15. The cast article according to claim 14exhibiting a casting microstructure comprising at least one or moreinsoluble solidified and/or precipitated particles with at least onealloying element selected from the group consisting of Al, Si, Mg, Fe,Mn, Zn, Sr, Ti, Zr, V, Cu, Ni.
 16. A method of manufacturing a highpressure die casting of an aluminum alloy, the method comprising:providing a molten aluminum alloy comprising: at least about 78 weightpercent aluminum (Al); about 7 to about 15 weight percent silicon (Si);about 0 to about 0.6 weight percent magnesium (Mg); about 0 to about 1weight percent iron (Fe); about 0 to about 1 weight percent manganese(Mn); about 0 to about 1.0 weight percent zinc (Zn); about 0 to about0.1 weight percent strontium (Sr); about 0 to about 0.5 weight percenttitanium (Ti); and about 0 to about 0.5 weight percent zirconium (Zr);casting the molten aluminum alloy into a die under high pressure;solidifying the alloy in the die to form the casting; cooling thecasting in the die to a quenching temperature; quenching the casting ina quenching solution; and subjecting the casting to at least oneage-hardening treatment.
 17. The method according to claim 16, whereinthe casting exhibits corrosion of less than about 0.1 mm/year.
 18. Themethod according to claim 16, wherein the casting being as-cast,age-hardened by a temper T5 treatment, or age-hardened by a temper T5treatment and then soaked at 200° C. for 200 hours and tested at 200° C.exhibits a yield strength above about 150 MPa, ultimate tensile strengthabove about 190 MPa, and strain above about 1.8 percent.
 19. The methodaccording to claim 16, wherein the casting is subject to solution heattreatment for a time from about 5 minutes to about 25 minutes.
 20. Amethod of manufacturing a high pressure die casting of an aluminumalloy, the method comprising: providing a molten aluminum alloyconsisting essentially of at least about 78 to about 90 weight percentaluminum (Al), about 7 to about 15 weight percent silicon (Si), about 0to about 0.6 weight percent magnesium (Mg), about 0 to about 1 weightpercent iron (Fe); about 0 to about 1 weight percent manganese (Mn),about 0 to about 1.0 weight percent zinc (Zn), about 0 to about 0.1weight percent strontium (Sr), about 0 to about 0.5 weight percenttitanium (Ti), about 0 to about 0.5 weight percent zirconium (Zr), about0 to about 0.5 weight percent vanadium (V), about 0 to about 0.5 weightpercent copper (Cu), and about 0 to about 1 weight percent nickel (Ni);casting the molten aluminum alloy into a die under high pressure;solidifying the alloy in the die to form the casting; cooling thecasting still in the die to a quenching temperature; quenching thecasting in a quenching solution; and subjecting the casting to a T5age-hardening treatment, wherein the casting exhibits corrosion of lessthan about 0.1 mm/year and exhibits a yield strength above about 150MPa, ultimate tensile strength above about 190 MPa, and strain aboveabout 1.8 percent after the casting is soaked at 200° C. for 200 hoursand tested at 200° C.